Pci-6251 DAQmx reading VI average time

Hi, all
I am using PCI-6251 I have attached a VI and its profile data, I don’t really understand—the average time of DAQmx Read (Raw 1D I16).vi is 175.5ms, but the longest is 984.4ms, why the difference is so big? is there a way to reduce the difference?
Thanks
Lyn
Attachments:
Sava all sample.vi ‏138 KB
profile data.xls ‏130 KB

Hi Lyn,
I have taken a look over the code, there are various VI's that could be running at the same time as the DAQmx Read that your processor may be switching between (e.g. “Divide Data.vi”, “array max and min”). Have you considered implementing a producer consumer architecture? This would allow you to read the data off your DAQ card into a queue and process and/or save the data in another loop.
In addition you are opening and closing your file with every iteration of the loop which will not help the performance of your VI. I would suggest take the “TDMS Open” and “TDMS Close” VI’s out of the loop.
Best of luck with your application.
Kind regards,
Ben L
Field Engineer
National Instruments

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After much greif and trying a half dozen various drivers with various settings and other ideas the following procedure based on Caraval's advice worked first time with no errors and seemingly no functional issues. The system so far appears to be running in Windows 7 just as it was on Windows XP.
1. Install LabView from original install CDs, by opening the folder and right-clicking 'setup.exe' and clicking 'run as administrator'. Selected 'do not install drivers' during the install procedure. Rebooted computer.
2. Installed NI-DAQmx 8.9 from the self-extracting .zip file available here. Shutdown computer.
3. Removed power, pressed power button to completely discharge power supply. Installed PCI-6251 card.
4. Booted computer, and logged in. Waited a long time, Windows eventually saw new hardware and installed drivers. Verified MAX could see card.
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How to use counters of PCI 6251 to count the number of pulses

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I have inputs from an optical encoder {pulse train} and i need to count the number of pulses for a short period of time to estimate the speed of the DC motor. Could you please tell me how to use the counters in PCI 6251 DAQ. I found something on DAQ STC, whichs says the input pulse should be connected to PF0 {ctr source}, but i have query where do i get the output {number of pulses counted in a particular period of time}.
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Hi bsnr,
Thanks for the post!
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Posttriggered DAQmx Read output if no trigger received.

I am running a posttriggered analog voltage input on a PCIe-6251 via DAQmx and I need to know what voltage Labview bins if no posttrigger is received and I set the timeout response to "cancel error on match."

MikeK,
I am not sure what you mean by post-triggered. Are you referring to a reference trigger, which keeps a buffer of data so that after it is triggered that buffer of data can still be recorded?
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DAQmx: Numerical indicators go blank intermittently using DAQmx Read

Hello everyone,
I was wondering if anyone else has ever fought this issue and won. I have a loop (I will attempt to attach an image of the block diagram) which performs a DAQmx Read operation. The loop employs a 200 millisecond wait. The loop scales the data, sends all of the values to little indicators in an array, picks out a few critical values to display on duplicate large indicators, and optionally logs the data by streaming it to disk. The task will usually (99.9% of the time) be run at 100Hz. So, I was figuring I could do a "Read All", since at 200 ms of wait time due to the millisecond multiple wait function, I should always have around 20 points to read in the buffer the next time around. This would allow me to have very current readings in my displays. I could do a partial read, but then I figure I would have a lag between the displayed values and the reality of what's going on in the test. Having current readings, as current as can be, is highly desirable for this application.
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Sorry if I am too wordy. I have been accused of that before. I just notice a lot of "Help! DAQ doesn't work. How do I fix?" posts, and I don't see how I or anyone else could help that person at all.
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Attachments:
Log Monitor Block.JPG ‏292 KB

Yeah, as you and Erik said, just specifying (Sample Rate / 5) as the '# to read' could do the trick. Then you can ditch the 'Wait (msec multiple)' function. I don't think I'd recommend the -1 = infinite timeout though. I'm pretty leery of stuff that can lead to an infinite wait or an infinite loop. Even a 1 sec timeout should easily be way more than enough. Note however that this method depends on all your processing code executing in under 200 msec on average. Otherwise, your reads will fall behind and you'll eventually get a DAQ buffer overflow error. My earlier suggestion to first query for # available samples and then read the MAX of (# available, SampleRate/5) will prevent cumulative fall-behind effects.
There's too many unknowns to speculate with any confidence on exactly why the software timing method didn't work. I can point out some additional things that bear greater scrutiny though.
1. You've got some sort of function dealing with file streaming that takes a path input and produces a path output. This probably means that every loop iteration you're using the path to open a file, write data, and close the file again. This actually may consume more than 200 msec, at least some of the time. Because this runs in parallel with the msec wait function, something like the following could be happening:
A. Iteration 1 proceeds as expected. The DAQ read collects 20 samples, the file write consumes only 100 msec, and the wait msec function ends after 160 msec in order to end on a 200 msec multiple. The wait function took longest, so your whole loop ends on a 200 msec multiple.
B. On iteration 2, the wait msec function ends after 200 msec on the next 200 msec multiple. The DAQ read collects another 20 samples (because it's been pretty much exactly 200 msec since the previous loop iteration started) right away. However, Windows was busy messing with the file cache so this time your file write consumes 375 msec. The file function took longest so your whole loop ends 175 msec into the next 200 msec multiple.
C. On iteration 3, the wait msec function ends after 25 msec on the next 200 msec multiple. The DAQ read collects 37 samples that have come in since the prior call 375 msec ago. The file function consumes only 50 msec this time, ending the loop 25 msec into the next 200 msec multiple.
D. On iteration 4, the wait msec function ends after 175 msec at the next 200 msec multiple. The DAQ read collects the 5 samples that have come in since the prior call 50 msec ago. Uh oh, not enough samples...
One possible fix is to open the file outside the loop and leave it open until after the loop is done. Opening and closing files has quite a lot of overhead. Inside the loop, you'd be passing around the file refnum. Doing this one thing alone might also be a way to fix your timing problem. Along similar lines, you could write the data to a queue and then do your file writes in an independent loop that reads the data out of the queue. You can search here for "producer consumer" for more info.
-Kevin P.

Error -200279 at DAQmx read

Hi i am fairly new to daq in labview,
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Attachments:
Copy of NI 435x Thermocouple (LEE).vi ‏124 KB

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Attachments:
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Pci-6251 DAQmx reading VI average time

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